Weld Geometry Research Articles

Numerical and Experimental Investigation of Heat Distribution and Residual Stress Variation on Stacked Thin Sheets of CRNO Electrical Steel Post Tungsten Inert Gas and Cold Metal Transfer Welding

Abstract The paper presents a numerical and experimental investigation on the stacking of thin, cold rolled nongrain-oriented (CRNO) electrical steel sheets post-tungsten inert gas (TIG) and cold metal transfer (CMT) welding for predicting the effects of TIG and CMT welding current on weld geometry, temperature field, and residual stress distribution in thin, stacked weld sheets. Numerical simulation of a transient nonlinear thermal three-dimensional (3D) element based on actual weld conditions was carried out using ansys software by employing a moving heat source model based on a 3D Gaussian distribution to predict changes in temperature. As a result of the thermal history provided by the model, a mechanical analysis is performed to determine the residual stress distribution and the surface distortion in the element. A significant increase in weld penetration and weld width of the samples was observed with the increase in welding current, as well as a change in the temperature field in the weld zone. Moreover, both the experimental and numerical data are consistent in their estimation of the generation of residual stresses in the weld samples. A numerical model is presented for predicting the thermomechanical behavior of TIG and CMT welded stacked CRNO structures in the stator core of electric motors.

Influence of Scandium on AA5052-H32/AA5083-H111 TIG welded joint

ABSTRACT In the present work, two aluminum alloys 5052-H32 and 5083-H111 were tungsten inert gas welded using ER5356 filler and scandium added modified ER5356 filler rod. The morphologies of the weld joints were analyzed and characterized for microstructure and physical properties by optical microscopy, scanning electron microscopy, tensile testing and Vickers` microhardness survey. The scandium from the modified filler rod was found to fuse with aluminum of the base alloy plates in the weld zone and enhanced the yield strength of the joint by 46 MPa. The corresponding increase in ultimate tensile strength was observed to be 48 MPa. The improved strength rates were attributed to the formation of aluminum – scandium dispersoids that effectively restrained the recrystallization and growth of grains, greatly enhancing the weld joint performance. The resulting scandium added weld joint had excellent weld geometry while exhibiting active control over intermetallic compound within the material fusion zone. The ultimate tensile strength and microhardness of this joint were enhanced considerably.

Analysis of Controlled Driving and Spreading Behavior of Molten Pool in Cold Metal Transfer

The controlled short-circuit transfer is used to control the heat input of the molten pool and the base metal in the cold metal transfer welding process, including droplet formation, droplet transfer and molten pool flow. Based on the influence of arc pressure on the surface of the molten pool, droplet impact and residual energy on the flow behavior of the molten pool, this research proposes the arc pressure driving model, the droplet impact driving model and the residual energy transfer model on the molten pool surface respectively, and on this basis, a theoretical model of controlled driving and spreading of the cold metal transition bath is proposed. The theoretical relationship between the surface shape of the keyhole and the driving force, and the relationship between the surface shape of the molten pool and the welding current are established. The model accurately predicts the formation width and contact angle of the molten pool in a specific interval, which can better control the welding process and geometry.

Influence of Air Gap Size to Mechanical Properties of Laser Welded Lap Joints

The paper is focused on the effects of air gap size to mechanical properties of laser welded lap joints. Structural steel plates of 3 mm thickness were used in the laser welding experiments. The laser welding experiments were conducted at two very different energy inputs (EI) of 60 and 320 J/mm. The weld geometries were investigated using optical microscopy. The shear strength of the lap joints was evaluated by uniaxial tensile tests. Results showed that with low EI of 60 J/mm the size of air gap had significant effect on the width of the interface as the larger air gap size increased the width of the interface. At high EI of 320 J/mm, the width of the weld at the interface did not change significantly as the air gap increased. The hardness of the weld metal was greater than the hardness of the base material at both EIs. The shear strength of the joint increased significantly with low EI of 60 J/mm, as air gap size increased. The size of the air gap did not have a large effect on the shear strength of the joint with higher EI of 320 J/mm.

Effect of collapse and hump on thermomechanical behavior in high-power laser welding of 16-mm marine steel EH40

This paper concerns high-power laser welding of thick plates for the ship industry. Thermomechanical behavior during laser welding of 16-mm marine steel EH40 using 25-kW laser power was investigated by a 3D finite element model. The objective is to analyze the effects of weld collapse and hump on the residual stress-induced thermal cycle. A double-cylindrical source model was proposed to simulate the transient distribution of temperature field. Heat flow distribution area is a cylinder, radial heat flow presents a Gaussian distribution, while heat flow peak in the direction of thickness is decaying then increasing exponentially. The predicted weld geometry had good agreement with the actual results. When collapse and hump were considered, simulation error of temperature distribution was only 1.54%. In addition, cooling curves obtained from the thermal simulation were incorporated into the continuous cooling transformation diagram of EH40 to explain the evolution mechanism of microstructure. It was shown that collapse and hump affected the values and distribution trend of residual stress in different thickness, especially in the high gradient stress zone near the weld center. The collapse mainly affects the residual stress distribution on the top surface, while the hump affects that on the bottom surface. Both of them have little influence on the residual stress in the middle thickness area. The cold contraction of weld metal and the stress concentration caused by weld shape during the cooling process are the fundamental reasons that collapse and hump affect the distribution of welding residual stress.

Metallurgical and Mechanical Properties of Fibrous Laser Welded Thick Q890 High Strength Low Alloy Steel with Varying Weld Geometries

Metallurgical and Mechanical Properties of Fibrous Laser Welded Thick Q890 High Strength Low Alloy Steel with Varying Weld Geometries

Numerical analysis and discussion on the hot-spot stress concept applied to welded tubular KT joints

Nominal stresses have been used for a long time for the assessment of fatigue resistance of welded joints, however, this approach has strong limitations since the definition of the nominal stress may be subjective for complex welded details and/or complex loading. On the other hand, the hot-spot stress approach has been proposed to overcome these limitations considering the structural geometrical discontinuities.However, the hot-spot stress methods also present certain limitations, and the present study aims at evaluating the available numerical and analytical hot-spot stress methods proposed by DNVGL (2016) and IIW (2014). The particular case of an offshore tubular KT joint has been considered herein and discretized in two planes. It has been studied numerically using the ABAQUS software coupled with the hot-spot stress extrapolation methods described in IIW (2014) and DNVGL (2016). The influence of the weld geometry has been considered and evaluated. In addition to the numerical method, the present study has also considered the analytical approach proposed in DNVGL (2016) derived from the combination of Efthymiou solutions for the stress concentration factor with the method of superposition of stresses. The numerical models according to IIW (2014) have been found to be more conservative when compared with the mesh-size methods proposed by DNVGL (2016), both in numerical modelling without the weld or with weld. For the numerical models with weld cord, the mean values of normalized difference index obtained for all braces together, as a result of comparing numerical results with analytical solutions, are lower, when compared with results obtained from the numerical models without weld cord.

Effect of ambient pressure on laser welding of AlSi10Mg fabricated by selected laser melting

This work attempted to introduce high pressure to reduce pore generation in laser welding of selective laser melted AlSi10Mg, which is different from the traditional approach where the vacuum was preferred in laser welding of aluminum alloys. To understand these phenomena, the impacts of laser welding parameters and ambient pressure on the porosity and weld geometry were examined. Porosity ratio was found linearly increasing with the laser power or linear energy. High-speed imaging revealed that the large pores were formed by multiple merging of small pores, which explained the decrease in fine porosity (<20 μm) but increase in coarse porosity (50–100 μm) when increasing laser power or linear energy. The vacuum ambiance significantly enlarged the pores (up to ∼400 μm) and formed narrow and deep welds. As pressure increased from 0.1 MPa to 0.4 MPa, the porosity ratio was dramatically decreased from ∼10.2% to ∼2.3% accompanied by a decline in porosity size and weld penetration depth. Numerical simulation results revealed that the shallowed weld penetration under high-pressure ambiance was attributed to the decreased recoil pressure, and the reduced porosity ratio was resulted from the high pressure which limited pore growth and merging.

Determination of notch factors for transverse non-load carrying stiffeners based on numerical analysis and metamodeling

Stress concentration factors (SCFs) at weld toes and weld roots as required for the effective notch stress concept (see [1, 2]) are usually computed using finite element analysis (FEA) which requires a certain amount of effort for model generation, the solving process, and postprocessing. Regression functions of many FEAs within given parameter bounds provide the possibility of a fast prediction of SCFs. This paper provides new and accurate regression formulae for the estimation of notch stresses at idealized weld geometries on the basis of multiple linear-elastic FEAs for the transverse stiffener (non-load carrying T-joint) under tension and bending of the load carrying slab. Regression of sampled finite element results has been performed using (a) second-order polynomial regression with coupling terms (PRC) and (b) artificial neural networks (ANN). The presented formulae are compared with several existing estimations of stress concentration factors. The new methods appear to show a higher quality of prognosis as well as apply to significant larger ranges of the geometrical parameters of the weld joint. The formulae presented here for the transverse stiffener add another welded joint to a series of similar surrogate models presented from Munich University of Applied Sciences in earlier publications and made available for use by the web-based tool SCF-Predictor.

Damage-Based Assessment of the Fatigue Crack Initiation Site in High-Strength Steel Welded Joints Treated by HFMI

This study aimed to identify the fatigue crack initiation site of high-frequency mechanical impact (HFMI)-treated high-strength steel welded joints subjected to high peak stresses; the impact of HFMI treatment residual stress relaxation being of particular interest. First, the compressive residual stresses induced by HFMI treatment and their changes due to applied high peak stresses were quantified using advanced measurement techniques. Then, several features of crack initiation sites according to levels of applied peak stresses were identified through fracture surface observation of failed specimens. The relaxation behavior was simulated with finite element (FE) analyses incorporating the experimentally characterized residual stress field, load cycles including high peak load, improved weld geometry and non-linear material behavior. With local strain and local mean stress after relaxation, fatigue damage assessments along the surface of the HFMI groove were performed using the Smith–Watson–Topper (SWT) parameter to identify the critical location and compared with actual crack initiation sites. The obtained results demonstrate the shift of the crack initiation most prone position along the surface of the HFMI groove, resulting from a combination of stress concentration and residual stress relaxation effect.

Deep Learning Based Inversion of Locally Anisotropic Weld Properties from Ultrasonic Array Data

The ability to reliably detect and characterise defects embedded in austenitic steel welds depends on prior knowledge of microstructural descriptors, such as the orientations of the weld’s locally anisotropic grain structure. These orientations are usually unknown but it has been shown recently that they can be estimated from ultrasonic scattered wave data. However, conventional algorithms used for solving this inverse problem incur a significant computational cost. In this paper, we propose a framework which uses deep neural networks (DNNs) to reconstruct crystallographic orientations in a welded material from ultrasonic travel time data, in real-time. Acquiring the large amount of training data required for DNNs experimentally is practically infeasible for this problem, therefore a model based training approach is investigated instead, where a simple and efficient analytical method for modelling ultrasonic wave travel times through given weld geometries is implemented. The proposed method is validated by testing the trained networks on data arising from sophisticated finite element simulations of wave propagation through weld microstructures. The trained deep neural network predicts grain orientations to within 3° and in near real-time (0.04 s), presenting a significant step towards realising real-time, accurate characterisation of weld microstructures from ultrasonic non-destructive measurements. The subsequent improvement in defect imaging is then demonstrated via use of the DNN predicted crystallographic orientations to correct the delay laws on which the total focusing method imaging algorithm is based. An improvement of up to 5.3 dB in the signal-to-noise ratio is achieved.

Prediction of fatigue failure in small-scale butt-welded joints with explainable machine learning

Butt-welded joints are common in many industries. The fatigue behavior of such joints depends on numerous factors, e.g. load level, local weld geometry, or parent material strength. To make things worse, these factors often interact, yet mutual influence can hardly be quantified by multivariate studies, i.e. varying one factor at a time out of many factors, due to the large number of required tests and the statistical nature of weld geometry. Consequently, fatigue assessment of such joints often deviates significantly between prediction and experimental result.Thus, alternative methods are desirable in order to take various influencing factors into account. To this end, machine learning techniques were used to predict failure locations and number of cycles to failure of fatigue tests performed on small-scale butt-welded joint specimens. In addition to accurate predictions, an understanding of importance and mutual influence of the factors is desired, e.g. a ranking of the most important factors; however, capturing the influence of several possibly interacting factors usually requires complex nonlinear machine learning models. We used gradient boosted trees. Since these are black box models, the SHapley Additive exPlanations (SHAP) framework was used to explain the predictions, i.e. identify influential features and their interactions. Lastly, the model explanations are linked back to domain knowledge.

Influence of laser spot oscillation parameters on the seam geometry and dilution in the LDNA process

The “Laser-assisted double wire with non-transferred arc surfacing process (LDNA)” is characterized by an electric arc burning between the filling wires. The molten filler material is fed to the substrate surface by gravity and is shaped by a laser beam. In this work, the influence of laser parameters on seam geometry and dilution is investigated. The investigations include a linear and convex pendulum form, a focal length of 300 mm and 400 mm, an oscillation frequency of 10 Hz and a disc laser using a wavelength of 1,030 nm with a power of 1,000 W and 1,400 W. Two 316L filling wires with 1.2 mm and an AISI1024 substrate with 20 mm are used. The change in the dilution and the welding geometry is determined.

Post-Treatment of Welding Joints of High Strength Steels II.:Improving Residual Stress Condition – Overview

High strength steel welding joints fatigue strength could be improved by changing the as weld condition with post-weld treatment. These post-weld treatments are classified to two categories which are the weld geometry and residual stress condition improvement methods. Post-weld treatment methods of high strength steel welding joints by improving weld geometry were overviewed in the first part of our article. The post-weld treatment methods for improving the welding joint residual stress condition are also applicable in high strength steels, but some consideration have to take in place when applying these techniques. The aim of this paper to review the welding joint residual stress condition improvement techniques considers application of these techniques in high strength steels.

Using the RSM method of improving process parameters of welding AISI 316 and nickel 201 using CO2 laser

The dissimilar butt welding of nickel 201 and AISI 316 was studied by utilising a 4 kW CO2 laser with the help of Response Surface Methodology (RSM). The effects of laser power are 2580–3420 W; welding speed 450–1150 mm/s; focal position –1 to 0 mm; beam angle 84–96 degrees; and beam offset 0–0.2 mm on weld geometry, i.e., depth of penetration, bead width, and the Fusion Zone Area (FZ). The required weld profile responses for dissimilar butt welding were modeled mathematically. The constructed models were tested using the sequential F-test, lack of fit test, and analysis of variance (ANOVA). Mathematical models are reflected in the output answers within the parameters of the input process. This laser welding process with an optimal condition zone was discovered using a numeric optimization technique. It aids in the optimization of this process’s regulated responses by allowing for more effective parameter combinations. It is clear from the tensile test results that the expected weld strength has been achieved. There is some delta ferrite found in the interdendritic zone in the microstructure and the solidification process reveals columnar grains.

A brief review on the Tube-to-Tube plate welding process

Weld settings play an awfully important part in influencing the standard of welded joints. The joint standard is defined as supported properties like weld geometry, mechanical characteristic, and deformation. Usually, all welding processes get a welded joint with the specified welding parameters, perfect mechanical characteristics, and minimal deformation. Today, applying the design of experiments (DoE), evolutionary formulas, and computational networks is widely wont to improve the mathematical relationship between the welding process's input settings and the weld joint's output variables to see the weld quality required cause weld input parameters. This text presents a comprehensive review of the literature on the appliance of those methods within the field of welding. The revision is classed in line with the output characteristics of the weld, that is, the weld's geometry and the weld's mechanical properties.

Laser welding of L-PBF AM components out of Inconel 718

With regard to efficient production, it is desirable to combine the respective advantages of additively and conventionally manufactured components. Particularly in the case of large-volume components that also include filigree or complex structures, it makes sense to divide the overall part into individual elements, which afterwards have to be joined by welding.The following research represents a first step in fundamentally investigating and characterizing the joint welding of Laser Powder Bed Fusion (L-PBF) components made of Inconel 718. For this purpose, bead-on-plate welds were performed on plates manufactured using the L-PBF process and compared with the conventionally manufactured material. Conventional laser beam welding was used as welding process. The weld geometry was investigated as a function of the L-PBF build-up orientation. It was found that the welding depth and weld geometry differ depending on this orientation and in comparison to the conventional material.

WeldNet: From 3D phased-array ultrasound scans to 3D geometrical models of welds and defects

Non-destructive testing techniques validate the structural integrity of materials. However, even though these techniques can recognize defects, they do not aim at identifying the shape of the structure itself. Considering that the location of welding defects determines how critical they are, being able to locate the weld and the defect would greatly enhance the analysis. This paper presents a two-step framework that identifies weld geometry and defects simultaneously and reconstructs the surface of the welded joint and the identified defects. The result is a 3D geometric model that adds more context to the analysis, improving the evaluation of the weld.

Numerical investigation of laser beam-welded AA2198 joints under different artificial ageing conditions

The present study aims to investigate the effect of weld geometry and geometrical shape imperfections on the mechanical behavior of welded joints under different post-weld heat treatment conditions. Finite element analyses were performed using the local mechanical properties of laser beam welded AA2198 joints obtained from micro-flat tensile test specimens. The finite element results show that, for the as-welded condition show that the maximum strain was observed in the lower region of the fusion zone, independently the geometrical imperfections. By applying post weld heat treatment, the maximum strain concentration can now be noticed in the upper region of the fusion zone for all the ageing times due to the lower local elongation at fracture values.

Numerical study of the influence of weld geometry variations on fatigue life using the notch stress analysis

Idealized geometry is typically used in standards for the fatigue life assessment of welded joints. In the presence of stochastic geometrical variations along the weld, the choice of the idealized geometry is however ambiguous. In the notch stress (NS) method with a fictitious notch radius rref = 1 mm, the FAT 225 curve is derived for welds with relatively good quality in toe profiles. In the NS method with rref = ractual + 1 mm, a lower FAT 200 curve is recommended. Both approaches neglect the stochastic variability in toe radius, toe angle and leg length along the weld. The aim of this paper is two-fold. First, a numerical comparison between both approaches in terms of their predicted fatigue life is performed for a non-load carrying fillet cruciform joints. The results show that the NS method with rref = 1 mm and FAT 225 is substantially more conservative. Second, these methods are enhanced by replacing the deterministic stress concentration factor by a probability distribution computed using Monte Carlo simulation. It is shown that NS with rref = 1 mm and FAT 225 does not predict any substantial influence of the stochastic variability in process parameters since the actual toe radius is not included in the analysis. However, the NS method with rref = ractual + 1 mm and FAT 200 predicts a decrease in fatigue life when uncertainties in geometrical parameters is included. This numerical study paves the way for an experimental validation of the predicted influence of stochastic variability of geometrical parameters based on the stochastic notch stress analysis.